Apply Finality to blocks prior to L1 Finality Singal (#13708)

* Apply Finality to blocks prior to L1 Finality Singal

* add Log when Finality is assumed from newer Finality Signal

Author: axelKingsley

op-supervisor/supervisor/backend/db/query.go

@@ -171,6 +171,28 @@ func (db *ChainsDB) Finalized(chainID types.ChainID) (types.BlockSeal, error) {
 	if finalizedL1 == (eth.L1BlockRef{}) {
 		return types.BlockSeal{}, fmt.Errorf("no finalized L1 signal, cannot determine L2 finality of chain %s yet", chainID)
 	}
+
+	// compare the finalized L1 block with the last derived block in the cross DB
+	xDB, ok := db.crossDBs.Get(chainID)
+	if !ok {
+		return types.BlockSeal{}, types.ErrUnknownChain
+	}
+	latestDerivedFrom, latestDerived, err := xDB.Latest()
+	if err != nil {
+		return types.BlockSeal{}, fmt.Errorf("could not get the latest derived pair for chain %s: %w", chainID, err)
+	}
+	// if the finalized L1 block is newer than the latest L1 block used to derive L2 blocks,
+	// the finality signal automatically applies to all previous blocks, including the latest derived block
+	if finalizedL1.Number > latestDerivedFrom.Number {
+		db.logger.Warn("Finalized L1 block is newer than the latest L1 for this chain. Assuming latest L2 is finalized",
+			"chain", chainID,
+			"finalizedL1", finalizedL1.Number,
+			"latestDerivedFrom", latestDerivedFrom.Number,
+			"latestDerived", latestDerivedFrom)
+		return latestDerived, nil
+	}
+
+	// otherwise, use the finalized L1 block to determine the final L2 block that was derived from it
 	derived, err := db.LastDerivedFrom(chainID, finalizedL1.ID())
 	if err != nil {
 		return types.BlockSeal{}, fmt.Errorf("could not find what was last derived in L2 chain %s from the finalized L1 block %s: %w", chainID, finalizedL1, err)